On the hard difficulty, the single player game lasted about 15 hours. If you decide to play on normal, you are probably looking at a 10 to 12 hour experience. The difficulty can be changed at any time during the game, but that will effect achievements. As stated earlier, the multiplayer features flesh out the game and can dramatically increase the replay time of the title. I highly recommend this game to any fan of the horror genre, FPS gamers, or those looking for an engrossing story filled with action. I would like to mention that watching through the entire credits sequence at the end of the single player game will help explain the final act. For those looking for just the single player game, rent the title to knock out the quick campaign. For everyone else interested in the multiplayer and the achievements, it's worth a purchase price of around $30 to $40.